Centrifuge permeameter for unsaturated soils system

ABSTRACT

The present invention includes an apparatus, method and centrifuge permeameter system that includes a hydraulic permeameter adapted for use in a centrifuge; and an automated data acquisition system, wherein the centrifuge permeameter non-destructively determines one or more soil characteristics from a sample of granular material such as soil, rock, and concrete when centrifuged.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 60/634,189, filed Dec. 8, 2004, the contents of which areincorporated by reference herein in their entireties.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of permeameter,and more particularly, to a centrifuge permeameter that allowscontinuous, non-destructive and non-intrusive measurements of relevantvariables.

BACKGROUND OF THE INVENTION

This invention was made with U.S. Government support under Contract No.CMS-0094007 awarded by the NSF. The government may own certain rights inthis invention. Without limiting the scope of the invention, itsbackground is described in connection with soil permeameters.

For example, U.S. Pat. No. 4,679,422, issues to Rubin, et al., disclosesa method and apparatus for steady-state measurement of liquidconductivity in porous media. U.S. Pat. No. 6,634,876, issued toSchofield, discloses centrifuges and associated apparatus and methods.

U.S. Pat. No. 6,810,755, issued to Pask, et al., for a permeametersystem and method to determine soil hydraulic capacity for onsitewastewater systems. The permeameter has a hollow tube with a second tubeslidably disposed within an internal chamber of the hollow tube and isused in combination with one or more tables to correlate a specific rateof reading fall rate of water to the soil hydraulic capacity of the soilbeing tested. A conventional measuring tape is affixed to the outsidesurface of the hollow tube such that the numbers extend vertically alongthe length, or longitudinal central axis, of the hollow tube. Thepermeameter is used in combination with one or more charts thatcorrespond with soil hydraulic capacity. The charts are created byformulas defined using known soil absorption principals, the dimensionsof the permeameter, the dimensions of an auger hole in the soil, and thelevel of a water line in the auger hole.

Another permeameter is taught in U.S. Pat. No. 6,571,605, issued toJohnson. Johnson teaches a constant-head soil permeameter fordetermining the hydraulic conductivity of earthen materials, Theconstant-head soil permeameter is used to determine hydraulicconductivity of earthen materials in a borehole. The permeameter usesincludes a calibrated reservoir attached to a suitable length of hose.Water is added to the calibrated reservoir and allowed to flow freelyinto until an equilibrium level is reached in the borehole and insidethe soil permeameter. The water flowing to the permeameter is throttledby buoyant float pressure, thereby allowing better constant head controland much greater depths of testing than previously attained by knownpermeameters. The permeameter may also include a filtered vent system,backflow check valve, and seals. The filter system restricts entry ofsoil particles and debris, thereby minimizing cleaning and maintenanceof the invention. The soil permeability is determined based on theequilibrium height of water, rate of water flow, and dimensions of theborehole.

Yet another permeameter is taught in U.S. Pat. No. 6,655,192, issued toChavdar for a combined permeameter-porosimeter that measures normal andlateral permeability measurements on porous materials. The permeabilitymeasurements may be taken from compressed or uncompressed samples atroom or elevated temperatures. A wide variety of fluids or gas may beused to penetrate the test fluid depending on the application and theporosity of the sample. Briefly, the penetrating test fluid is forcedthrough the sample under pressure and the load, the fluid displacement,and the time are used to calculate the permeability, porosity, pore sizedistribution, average pore size and the number of pores per unit area.

Finally, U.S. Pat. No. 6,055,850, issued to Turner, et al., teaches amulti-directional permeameter that is used to determine the coefficientsof permeability using a constant (or falling) head method for thelaminar flow of a fluid (e.g., water), through a specific material ortest sample. The apparatus is a mold secured to a base, a lid is securedto the mold, inlet and outlet ports allow fluid flow to occur in boththe horizontal plane and the vertical plane to determine thecoefficients of permeability of a particular sample either horizontally,vertically, or simultaneously horizontally and vertically.

SUMMARY OF THE INVENTION

The present invention is an apparatus, method and system for acentrifuge permeameter that allows continuous, non-destructive, andnon-intrusive measurement of relevant hydraulic variables (suction,moisture content, fluid flow rate) in a single specimen while in-flightin the centrifuge. The centrifuge permeameter allows a user to obtain anaccelerated definition of the fluid retention curve and hydraulicconductivity function, simultaneously. The present inventors recognizedthat current testing methods used to define the unsaturated hydraulicproperties often require the use of several specimens, significanttesting times, and destructive or intrusive measurement of thevariables.

Furthermore, it was found that available technologies do not allowdetermination of the fluid retention curve and hydraulic conductivityfunction simultaneously. Also, current centrifuge technology does notallow the direct acquisition of the relevant variables (e.g., suction,moisture content, fluid flow rate) in-flight during testing. Thetime-consuming nature of current conventional technology and its effecton test data, results in inefficient use of resources and limitedusefulness for the data gathered.

For example, determination of the hydraulic properties for alow-permeability clay specimen may take over one year (more than onemonth for each data-point in either the fluid retention curve orhydraulic conductivity function). Permeability information is obtainedin a few days with the centrifuge permeameter disclosed herein.

The present invention permits the simultaneous determination of thefluid retention curve and hydraulic conductivity function for soil,rock, or concrete. Overall, the apparatus, system and method may be usedfor low-hydraulic conductivity materials, the hydraulic properties ofwhich cannot be obtained in a practical manner using currently availabletechnology. In addition, the apparatus, system and method encourages theuse of experimentally obtained hydraulic properties for practicalproblems, instead of the currently used analytical predictions.

The present invention includes a centrifuge permeameter system andmethod of use in which a hydraulic permeameter is adapted for use in acentrifuge and is in communication with an automated data acquisitionsystem that detects one or more soil characteristics from a soil sampleconnected to the hydraulic permeameter. The automated data acquisitionsystem non-destructively determines one or more soil characteristicsfrom a soil sample of porous material such as soil, rock, and concretewhen centrifuged. The one or more soil characteristics may be selectedfrom variables including: suction, moisture content, hydraulicconductivity and the relationship between one or more of thesevariables. Examples for use of the permeameter include geotechnicalengineering (e.g., fluid flow and mechanical analyses), hydrology (e.g.,groundwater recharge calculations), agriculture (e.g., plant-soilinteraction analysis), environmental engineering (e.g., contaminanttransport analyses), and petroleum engineering (e.g., oil reservoircharacterization).

The permeameter is designed to control the inflow and outflow boundaryconditions to generate open-flow boundary conditions that do notinterfere with the ongoing flow process. Generally, the inflow andoutflow boundary conditions will not impose a suction value onto thespecimen. Furthermore, the one or more inflow boundary condition and oneor more outflow boundary condition may be selected to permit the suctionand moisture content to attain any value in equilibrium with an ongoingflow process controlled by a fluid flow rate imposed on the sample. Thepermeameter instrumentation may continuously and nondestructivelymeasure one or more variables relevant to unsaturated fluid flow throughsoils while the centrifuge is in flight. Examples of the values that theautomated data acquisition system may continuously measure include,e.g., one or more of the following: moisture content, suction,temperature, relative humidity, specimen weight and combinations orvariations thereof.

Another embodiment of the invention is a centrifuge permeameter systemwith an automated data acquisition system for measuring unsaturated soilcharacteristics that includes a permeameter that applies a fluid flowrate less than the saturated soil hydraulic conductivity to at least oneportion of a soil specimen and controls the inflow and outflow boundaryconditions to generate open-flow boundary conditions. The one or moresoil characteristics is selected from variables including suction,moisture content and hydraulic conductivity and from the relationshipbetween these variables and may be used for fluid flow and mechanicalanalyses, groundwater recharge calculations, plant-soil interactionanalyses, contaminant transport analyses and oil reservoircharacterization.

The present invention also includes a method of measuring unsaturatedsoil characteristics by placing a soil sample in a centrifugepermeameter, applying a centripetal acceleration to the soil specimen,applying a low-flow rate to at least one side of the soil specimenduring centrifugation, controlling inflow and outflow boundaryconditions within the permeameter to generate open-flow boundaryconditions; and continuously measuring one or more characteristics ofthe soil sample while in flight. The centripetal acceleration applied tothe soil specimen is selected to permit the suction and moisture contentto attain equilibrium with an ongoing flow process. Generally, theinflow and outflow boundary conditions in the permeameter are selectedto permit the suction and moisture content to attain any value inequilibrium with the ongoing flow processes. The permeameter willcontinuously and/or nondestructively measure the variables relevant tounsaturated fluid flow through soils, while the centrifuge is in flight.

Another embodiment of the present invention is a permeameter made from acylinder having at least one window for visual inspection positionedbetween an inflow end of the cylinder and an outflow end of thecylinder. A fluid distribution cap is disposed at the inflow end of thecylinder and a porous sample support cap disposed at the outflow end ofthe cylinder and one or more primary outflow fluid collection reservoirsdisposed within the cylinder. The one or more primary outflow fluidcollection reservoirs are disposed about the cylinder includes one ormore pore water pressure transducers to measure outflow volume withinthe cylinder; and a pinhole at the outflow reservoir to prevent build-upof air pressures in the outflow reservoir. The permeameter is adapted tooperation within a centrifuge. The permeameter may also include one ormore ports disposed about the cylinder to permit contact between the oneor more ports and the soil sample to measure a suction profile.

The permeameter may also include one or more time domain reflectometry(TDR) probes at least partially within or about the cylinder to measurethe average moisture content in the soil sample. In one embodiment, thepermeameter is supported within the centrifuge on one or more weighingdevices that monitor the weight of the permeameter. The centrifugepermeameter may also include a secondary overflow outflow fluidcollection reservoir disposed in communication with the one or moreprimary outflow fluid collection reservoirs having one or more pressuretransducers to measure outflow volume and a pinhole at the reservoir toprevent build-up of air pressures in the outflow reservoir. Thepermeameter instrumentation continuously and/or nondestructivelymeasures one or more variables relevant to unsaturated fluid flowthrough soils while the centrifuge is in flight.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of thepresent invention, named the Centrifuge Permeameter for UnsaturatedSoils (CPUS), reference is now made to the detailed description of theinvention along with the accompanying figures in which:

FIG. 1A is a graph of the fluid retention curves for different soils,and FIG. 1B is a graph of the hydraulic conductivity functions fordifferent soils;

FIGS. 2A and 2B show the details of a rotary fluid union;

FIGS. 3A to 3C show the details of an inflow fluid distribution cap;

FIGS. 4A to 4H show the details of a swing-type CPUS shrink/swellpermeameter;

FIGS. 5A to 5C show the details of a swing-type CPUS hydrauliccharacterization permeameter;

FIG. 6A and 6B show the details of a stationary CPUS prototypepermeameter; and

FIGS. 7A to 7F show top and isometric views of the CPUS permeameterarrangements in the centrifuge.

DETAILED DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the presentinvention are discussed in detail below, it should be appreciated thatthe present invention provides many applicable inventive concepts thatcan be embodied in a wide variety of specific contexts. The specificembodiments discussed herein are merely illustrative of specific ways tomake and use the invention and do not delimit the scope of theinvention.

To facilitate the understanding of this invention, a number of terms aredefined below. Terms defined herein have meanings as commonly understoodby a person of ordinary skill in the areas relevant to the presentinvention. Terms such as “a”, “an” and “the” are not intended to referto only a singular entity, but include the general class of which aspecific example may be used for illustration. The terminology herein isused to describe specific embodiments of the invention, but their usagedoes not delimit the invention, except as outlined in the claims.

As used herein the term “prototype” denotes the scaled relationshipbetween a small-scale specimen in the centrifuge and a large-scaleearthen structure in the nature (e.g., dams, embankments, landfills,slopes, etc.).

The present invention is an apparatus, method and system for determiningthe hydraulic properties of porous materials. As mentioned, the systemis a Centrifuge Permeameter for Unsaturated Soils (CPUS). The CentrifugePermeameter is used to define the unsaturated hydraulic properties ofporous materials such as soil, rock, and concrete.

The present invention provides a centrifuge permeameter system having apermeameter adapted for use in a centrifuge and an automated dataacquisition system. The automated data acquisition system may be used todetect one or more soil characteristics from a soil sample connected tothe hydraulic permeameter. The automated data acquisition system mayinclude a CPU or a computer and may store data internally or externallyand/or the data may be displayed or printed. The automated dataacquisition system may be connected to other systems, main frames,printers, plotters or storage devices via direct connections, wificonnections, Bluetooth connections, IR connections, laser connections orother communication mechanism. In addition to the recording andprocessing of data by the automated data acquisition system, it may beused to control other parameters of the present invention.

The centrifuge permeameter non-destructively determines one or more soilcharacteristics from a sample of porous material such as soil, rock, andconcrete when centrifuged. The one or more soil characteristics mayinclude suction, moisture content, hydraulic conductivity and therelationship between these variables and the permeameter controls theinflow and outflow boundary conditions to generate open-flow boundaryconditions by applying a fluid flow rate to at least one side of a soilspecimen. Additionally, the permeameter further includes a fluid inflowdistribution cap that does not impose a suction value onto the specimen.The inflow and outflow boundary condition are selected to permit thesuction and moisture content to attain specific values at equilibrium,with an ongoing flow process that is controlled by a fluid flow rateimposed on the sample. The automated data acquisition system maycontinuously measures one or more values, e.g., moisture content,suction, temperature, relative humidity, fluid inflow rate, fluidoutflow rate, specimen weight and combinations thereof

A method of measuring unsaturated soil characteristics is also provided.A soil specimen is placed in a centrifuge permeameter and a centripetalacceleration to the soil specimen. A low-flow rate is applied to atleast one side of the soil specimen during centrifugation and theoutflow boundary conditions within the permeameter are controlled togenerate an open-flow boundary condition. The characteristics of thesoil specimen are continuously measured while in flight.

The automated data acquisition system continuously measures one or moresoil characteristics from an unsaturated soil specimens, e.g., moisturecontent, suction temperature, fluid inflow rate, fluid outflow rate,steady-state fluid flow, specimen weight, evaporation and combinationsthereof The centripetal acceleration applied to the soil specimen isselected to permit a suction and a moisture content to attainequilibrium with an ongoing flow and the inflow and outflow boundaryconditions in the permeameter permit the suction and moisture content toattain any value in equilibrium with the ongoing flow processes. Dry airor heat may be applied to the soil specimen to induce moistureevaporation while continuously and nondestructively measuring relevantvariables such as the change in temperature, relative humidity, andsmall changes in the weight of a soil specimen while in flight.

The present invention also provides a permeameter adapted to operatewithin a centrifuge. The permeameter includes a cylinder having at leastone window for visual inspection positioned between an inflow end of thecylinder and a outflow end of the cylinder. A fluid distribution cap isdisposed at the inflow end of the cylinder and a porous sample supportcap is disposed at the outflow end of the cylinder. The permeameterincludes a primary fluid outflow collection reservoirs disposed aboutthe cylinder which has one or more fluid pressure transducers to measureoutflow volume and a pinhole to prevent build-up of air pressure in theoutflow reservoir. The centrifuge permeameter of also includes two ormore ports disposed about the cylinder to permit contact between one ormore heat dissipation units (HDU) probes and the soil sample to measurea suction profile and/or one or more time domain reflectometry (TDR)probes at least partially within, the cylinder to measure the averagemoisture content in the soil sample.

Unsaturated hydraulic properties include the relationships betweensuction and moisture content (the fluid retention curve), and suctionand hydraulic conductivity (the K-function), examples of which are shownin FIGS. 1A and 1B for different porous materials. FIG. 1A is a graphthat shows the fluid retention curve for different materials and FIG. 1Bis a graph that shows the K-functions for different materials, which aredetermined concurrently, in flight using the present invention.

These properties are necessary information in several fields, includinggeotechnical engineering (fluid flow and mechanical analyses), hydrology(groundwater recharge calculations), agriculture (plant-soil interactionanalysis), environmental engineering (contaminant transport analyses),and petroleum engineering (oil reservoir characterization.) TheCentrifuge Permeameter incorporates the use of a low-flow hydraulicpermeameter and a centrifuge to obtain these important materialproperties. The hydraulic permeameter is able to control the fluid flowrate and boundary conditions within a material specimen. By placing aspecimen within the hydraulic permeameter under a centripetalacceleration in the centrifuge (which may be considered to be anincreased gravitational field), the driving force for fluid flow rate isincreased, which results in a quadratic decrease in the time required toreach steady-state fluid flow conditions. Consequently, the unsaturatedhydraulic properties such as the fluid retention curve and theK-function can be obtained from a single specimen in a comparativelyshort period of time. An important feature of the Centrifuge Permeameteris that the relevant variables (suction, moisture content, fluid flowrate) are obtained continuously while testing the specimen in-flightwithin the centrifuge. This permits measurement of transient flowprocesses without changing the acceleration field (i.e., by stopping thecentrifuge) in order to make measurements.

The Centrifuge Permeameter allows continuous, non-destructive, andnon-intrusive measurement of all relevant variables (suction, moisturecontent, fluid flow rate) in a single specimen while in-flight in thecentrifuge, to obtain an accelerated definition of the fluid retentioncurve and K-function simultaneously. Current testing methods used todefine the unsaturated hydraulic properties often require the use ofseveral specimens, significant testing times, and destructive orintrusive measurement of the variables. Also, available technologies donot allow determination of the fluid retention curve and hydraulicconductivity function simultaneously. Current centrifuge technology doesnot allow the direct acquisition of the relevant variables (suction,moisture content, fluid flow rate) in-flight during testing. Thetime-consuming nature of current conventional technology must bestressed. For example, determination of the hydraulic properties for alow-permeability clay specimen may take over one year (more than onemonth for each data-point in either the fluid retention curve orK-function). The same level of detailed information may be obtained in afew days with the Centrifuge Permeameter disclosed herein.

The CPUS system is characterized by being able to continuously measurethe variables relevant to unsaturated fluid flow through soils while thecentrifuge is in-flight. These variables include moisture content (θ),suction (Ψ), temperature (T), inflow fluid

flow rate, fluid outflow rate, and specimen weight. These variables havebeen successfully measured using a prototype permeameter under 1-g andunder N-g in the centrifuge. The first three variables (θ, Ψand T) aremeasured using currently available equipment (e.g., time domainreflectometry probes, heat dissipation units, and thermocouples,respectively). The centrifuge component of the CPUS system has a dataacquisition system, discussed later, has the capability of monitoringthese variables continuously.

In addition, CPUS system is characterized by applying a fluid flow rateto one side of a specimen and by properly controlling the inflow andoutflow boundary conditions at the top and bottom of the permeameter. Aparticular set of boundary conditions are used in this system, referredto as open-flow boundary conditions. These boundary conditions permitthe suction and moisture content to achieve equilibrium whilecontrolling fluid flow processes. This is in contrast to fixed boundaryconditions that maintain a particular value of suction or moisturecontent at the top and bottom of the permeameter.

The fluid inflow rate may be under the control of an infusion pump (notshown), and a low-flow hydraulic rotary fluid union that passes thefluid from the stationary environment to the spinning centrifugeenvironment. The minimum and maximum flow rates for the infusion pumpare about 1 to about 100 ml/hr. A rotary fluid union is necessarybecause conventional flow pumps cannot be used within a centrifuge dueto the high gravity forces and space limitations. In addition, thelocation of the pump outside the centrifuge allows direct monitoring ofthe fluid inflow rate and total volume infused. A peristaltic pump isalso available for this application, which has a minimum flow rate is0.18 ml/hr and a maximum flow rate of 200 ml/hr. However, an infusionpump is more suitable for use with a low-flow hydraulic rotary fluidunion as the peristaltic pump has a pulsating flow rate. The skilledartisan will recognize that other pumps may be used for thisapplication, which have a minimum flow rate of 0.1 ml/hr and a maximumflow rate of 300 ml/hr.

FIG. 2A shows a cross sectional view of the rotary fluid union with aninterface 12 that connects an upper chamber 14 (also referred to as astationary body), a lower chamber 16 (also referred to as a rotatingbody) and first fluid port 18 and second fluid port 20. The upperchamber 14 has two steel needles 22, while the lower chamber 16 has twoangled concentric channels the first concentric channel 24 and thesecond concentric channels 26. The lower chamber 16 is free to rotatearound the steel needles 22. Hydraulic lines (not shown) from theinfusion pump (not shown) are connected to the two inflow lines 28 atthe top of the rotary fluid union. Fluid moves into the steel needles 22attached to the upper chamber 14, then drips into the two angledconcentric channels 24 and 26 in the lower chamber 16. The fluid isconveyed via hydraulic lines (not shown) from the rotary fluid union tothe permeameter by centripetal force. Interface seals (not shown) areprovided to prevent fluid from moving from one of the two angledconcentric channels 24 and 26 to the other. The upper chamber 14 and thelower chamber 16 may be in contact through one or more bearings 30;however, other interfaces may be used to allow movement of the chambers.

FIG. 2B is a top view of the lower chamber 16 of the rotary fluid union.FIG. 2B shows the rotary fluid union with an interface 12 that connectsan upper chamber (not shown), a lower chamber 16 (also referred to as arotating body) and the first fluid port 18 and the second fluid port 20.The first fluid port 18 and second fluid port 20 are separated by one ormore drainage channels 32. Although, FIG. 2B depicts a single drainagechannel 32 between each of the first fluid port 18 and second fluid port20, the number of drainage channels 32 and the number of first fluidports 18 and second fluids port 20 may vary. In one embodiment, theupper chamber (not shown) and the lower chamber 16 are made of stainlesssteel or other like materials and the interface 12 may be alow-friction, low heat-generating material, e.g.,PolyTetraFluoroEthylene or sintered graphite. The skilled artisan willrecognize that the materials may be varied depending on the particularneeds of the specific application. For example, the upper chamber 14 andthe lower chamber 16 may be constructed of in part or entirely of metalsor alloys, e.g., copper, brass, iron, steel, chromolly, aluminum, etc.In addition, the upper chamber 14 and/or the lower chamber 16 may beconstructed of layers of materials, e.g., stainless steel layer on topof a aluminum layer on top of another stainless steel layer or afiberlayer (e.g., carbon fiber or fiberglass) layer under a metal layer.The materials may also be coated in some applications. Coating may beused to protect the parts, provide a non stick surface, provide atextured surface, etc.

FIGS. 3A is a bottom view of the inflow distribution cap 34. The upperboundary for the CPUS permeameter is a fluid inflow distribution cap 34,which ensures even distribution of fluid inflow to the top boundary ofthe specimen inside the permeameter. A hydraulic connection (not shown)consisting of plastic or flexible metal piping connects the low flowfluid union to the inflow distribution cap 34. The fluid flows into thereservoir (not shown) to a series of holes 38. The number and positionof the individual holes in the series of holes 38 may be varieddepending on the application.

FIGS. 3B and 3C show cross section views of the fluid inflowdistribution cap 34. Fluid flows into the reservoir 36 at the top of theinflow distribution cap 34 and then overflows from this reservoir 36into the series of holes 38 through a series of reservoir channels 40.These series of holes 38 are angled from the reservoir 36 to differentlocations on the bottom of the inflow distribution cap 34.

Furthermore, the dimensions of the present device vary depending on theparticular application. For example, the lower boundary for the CPUSpermeameter may be about 0.5 inch thick steel or acrylic supporting discwith a honeycomb pattern of 1/32inch holes; however, other dimensionsmay be used, e.g., the CPUS permeameter may be between about 0.1 and 1inch thick or greater than one inch thick and the holes may be betweenabout 1/64and about 1 inch. Furthermore, the holes do not need to be ofa uniformed size over the surface and may be varies and alternated asneeded. The inflow distribution cap 34 may be overlain by a porousfilter paper or a wire mesh to prevent clogging.

A shallow-sloped funnel (not shown) beneath the supporting disc (notshown) will drain fluid to a small hole (not shown) that leads to acollection reservoir (not shown). The amount of fluid in the collectionreservoir (not shown) (i.e., the outflow) is measured using a pressuretransducer (not shown). This is possible because the fluid pressure atthe base of the collection reservoir (not shown) is related to theheight of fluid in the collection reservoir (not shown), implying thatthe volume can be calculated from the fluid pressure (see FIGS. 5 and 6,herein below). For redundancy, the outflow collection reservoir may beremoved and weighed.

The CPUS system may also measure small changes in the weight of thespecimen for measurement of evaporation (not shown). Two methods havebeen developed: a load cell system and a device based on the principleof a manometer. Briefly, the connection between the permeameter and thecentrifuge rests upon an electronic load cell or a piston that transmitsthe weight of the specimen to a column of a dense fluid (e.g., mercury).The fluid column is calculated to have the same initial mass as theoriginal specimen (before fluid flow occurs). Accordingly, small changesin weight of the specimen within the permeameter due to evaporation areinferred by the electronic load cell or by how much the piston moves thecolumn of mercury, with the pressure in the mercury measured using apressure transducer.

The following discussions provide technical details for differentpermeameters that are used in the CPUS system. These include ashrink-swell permeameter used for assessing volume changes duringinfiltration and drying, a hydraulic characterization permeameter usedfor characterizing the fluid retention curve and K-function fordifferent materials, and a prototype permeameter used for modelingdifferent soil profiles expected in the field. To ensure that thegravity forces are always acting downward on the specimen, theshrink/swell permeameter and the hydraulic characterization permeameterare swing-type permeameters. The permeameters are attached to a rotatingrod that allows them to be vertical at 1-g and horizontal at N-g. Due tosize constraints, the prototype permeameter is fixed horizontally. Inaddition, some details concerning the specific centrifuge and the dataacquisition system are provided.

Shrink/Swell Permeameter. FIG. 4 shows a shrink/swell permeameter.Wetting of soils and other porous materials may cause swelling.Similarly, drying of soils and other porous materials may causeshrinkage. FIG. 4A shows a top view of the shrink/swell permeameter 42.The shrink/swell permeameter 42 allows the change in height of aspecimen to be measured during wetting and drying. The components of theshrink/swell permeameter 42 may include a cylinder 44. The cylinder 44may be, for example a about 3 inch tall by about 2.5 inch insidediameter with about a 0.5 inch wall thickness; however, the dimensionsmay be modified depending on the specific application . The cylinder 44may be made from acrylic, metal, plastic, polymers, resins or similarcomponents. The cylinder 44 has a supporting disc 46 that rests on ashelf (not shown). The supporting disc 46 may have 1/32inch holes withclose spacing; however the holes may be between about 1/64and about 1inch. Furthermore, the holes do not need to be of a uniformed size overthe surface and may be varies and alternated as needed.

FIG. 4B shows an elevation view of the shrink/swell permeameter 42illustrating the cylinder 44. FIG. 4C shows a bottom view of theshrink/swell permeameter 42. The components of the shrink/swellpermeameter 42 may include a cylinder 44 and a supporting disc 46 thatrests on a shelf (not shown). The supporting disc 46 may have 1/32inchholes with close spacing; however the holes may be between about 1/64andabout 1 inch. Furthermore, the holes do not need to be of a uniform sizeover the surface and may be varied and alternated as needed. FIG. 4Dshows a side view of the centrifuge holder 48 designed to fit theshrink/swell permeameter (not shown). FIG. 4E shows a cross sectionalview of the shrink/swell permeameter 42. The components of theshrink/swell permeameter 42 may include a cylinder 44 and a supportingdisc 46 that rests on a shelf 50. The supporting disc 46 may have aseries of holes 38.

FIG. 4F shows a cross sectional view of the shrink/swell permeameter 42having a sample placed therein. The components of the shrink/swellpermeameter 42 may include a cylinder 44 and a supporting disc 46 thatrests on a shelf 50. A sample of soil 52 is placed onto the supportingdisc 46 having a series of holes 38. FIG. 4G shows a cross sectionalview of the centrifuge holder 48 designed to fit the shrink/swellpermeameter (not shown). The centrifuge holder 48 has one or more vents54 positioned therein to allow for displacement. FIG. 4H shows a crosssectional view of the centrifuge holder 48 designed to fit theshrink/swell permeameter 42 having a sample 52 placed therein. Theshrink/swell permeameter 42 includes a cylinder 44 and a supporting disc46 that rests on a shelf 50. A sample of soil 52 is placed onto thesupporting disc 46 having a series of holes 38. The centrifuge holder 48has one or more vents 54 positioned therein to allow for displacement.The permeameter 42 is designed to fit in a centrifuge holder 48, whichis designed to be supported within a centrifuge (not shown). Vacuumgrease is applied onto the inside circumference of the cylinder toprovide a low friction, low permeability boundary between a specimen andthe cylinder.

A swelling test for the porous material in the shrink/swell permeametermay be conducted by: (i) placing a porous material into the permeametercylinder, resting atop the support plate (ii) spinning the centrifuge toa selected rotational velocity, (ii) commencing fluid inflow by settingthe infusion pump to a constant fluid flow rate, which causes fluid toflow through the rotary fluid union to the permeameter, (iii) observingthe changes in specimen height during fluid inflow due to swelling, and(iv) measuring the changes in specimen weight. The height of thespecimen may be measured visually, using a laser displacementtransducer, or a linearly variable displacement transformer (LVDT).Similarly, after performing a swelling test, a shrinkage test for theporous material in the shrink/swell permeameter may be conducted by: (i)stopping fluid flow, (ii) observing the changes in specimen heightduring fluid outflow due to shrinkage, and (iii) measuring the changesin specimen weight. The moisture content of the specimen may bedetermined using an oven at the end of the test. The moisture content atdifferent periods throughout the test may be back-calculated using themeasured values of specimen weight. The changes in height duringswelling and shrinkage may be correlated with the moisture content todetermine volume changes during wetting and drying.

Hydraulic Characterization Permeameter. FIGS. 5A-5C show a hydrauliccharacterization permeameter 56. The characteristics of the hydrauliccharacterization permeameter 56 are the constant fluid inflowapplication system and continuous, in-flight measurement of suction,specimen moisture content, and fluid outflow. The hydrauliccharacterization permeameter 56 measures the transient suction, moisturecontent, and fluid flow rate profiles through the specimen. It is alsoused to define when steady-state fluid flow conditions have beenachieved while in-flight in a centrifuge (not shown). This informationmay be used specifically to develop the relationships between thesuction, moisture content and hydraulic conductivity.

FIGS. 5A illustrates a top view of the hydraulic characterizationpermeameter 56. The hydraulic characterization permeameter 56 includes acylinder 58 is fitted with a fluid inflow distribution cap 34 having aTDR probe 60. In communication with the cylinder 58 is one or more heatdissipation units 62. FIGS. 5B show a cross sectional view of thehydraulic characterization permeameter 56. The hydrauliccharacterization permeameter 56 includes a cylinder 58 is fitted with afluid inflow distribution cap 34 having a TDR probe 60. In communicationwith the cylinder 58 is one or more heat dissipation units 62 throughthe one or more ports 64. A outflow support disc 66 is positioned belowthe cylinder 58 and in in communication with a fluid pressure transducer42 (PT) to measure the volume of fluid outflow. FIGS. 5C show anothercrossectional view of the hydraulic characterization permeameter 56. Thehydraulic characterization permeameter 56 includes a cylinder 58 isfitted with a fluid inflow distribution cap 34 having a TDR probe 60. Incommunication with the cylinder 58 is one or more heat dissipation units62. FIGS. 5B show a cross sectional view of the hydrauliccharacterization permeameter 56. The hydraulic characterizationpermeameter 56 includes a cylinder 58 is fitted with a fluid inflowdistribution cap 34 having a TDR probe 60. The TDR probe 60 extends intothe cylinder 58 vertically along the side of the cylinder 58 to measurethe average moisture content in the specimen (not shown), with the TDRprongs 48 embedded into the wall of the hydraulic characterizationpermeameter 56.

One embodiment of the hydraulic characterization permeameter 56 may be acylinder 58 with dimensions of 3 inches tall with 2.5 inches insidediameter and a 0.5 inch wall thickness. The cylinder 58 may also havedimensions of between about 1-5 inches tall with between about 1-6inches inside diameter and between about 0.25-1 inch wall thickness. Thecylinder 58 is made from acrylic to prevent electrical interaction withthe instrumentation; however other materials or coatings may be used inthe fabrication of the cylinder 58, metals, alloys, plastics, polymers,. In operation, fluid flow from an infusion pump (not shown) movesthrough the rotary fluid union (not shown) and enters the hydrauliccharacterization permeameter 56. Centripetal force generated by thespinning centrifuge (not shown) is used to accelerate fluid flow towardthe distal portion of the hydraulic characterization permeameter 56. Afluid inflow distribution cap 34 may be provided with an o-ring seal(not shown) to the cylinder 58 (e.g., acrylic) to ensure evendistribution of fluid over the specimen area. Placement of a pinhole(not shown) with a screw seal (not shown) allows air escape whichprevents air pressure build-up during fluid inflow. The hydrauliccharacterization permeameter 56 may also have an outflow support disc66, which may also include an o-ring seal to the permeameter cylinder 58to prevent leakage. The outflow support disc 66 may be a 0.25 inch steelor acrylic plate with honeycomb mesh of 1/32inch holes; however theoutflow support disc 66 may be between about 0.1 and 0.75 inches andconstructed from metals, alloys, composites, polymers, plastics orsimilar materials and either coated partially, entirely or uncoated. Ahole (not shown) beneath the support disc allows water to enter aprimary outflow collection reservoir (not shown) without allowing fluidfrom flowing back into sample (not shown) when a centrifuge (not shown)is at rest. A primary fluid outflow collection reservoir includes one ormore ports 62 for the placement of a fluid pressure transducer 68 (PT)used to measure the volume of fluid outflow. The collection reservoir isdetachable for weighing. A pinhole with a screw seal (not shown) isprovided to allow air escape (e.g., to prevent buildup of air pressureduring fluid flow into the outflow collection reservoir), located on theupper side of the collection reservoir to prevent fluid leakage whencentrifuge is at rest. One or more ports 62 are disposed along thecylinder 58 for instrumentation to allow heat dissipation units 64 to bein contact with the soil (not shown) to measure the suction distributionin the specimen (not shown). As seen in the cross-sectional insert ofFIG. 5C, a TDR probe 60 is placed vertically along the side of thecylinder 58 to measure the average moisture content in the specimen (notshown), with the TDR prongs 70 embedded into the wall of the cylinder58.

A typical test may be conducted in the hydraulic characterizationpermeameter 56 by: (i) spinning the centrifuge to a selected rotationalvelocity, (ii) commencing fluid inflow by setting the infusion pump (notshown) to a constant fluid flow rate, which causes fluid to flow throughthe rotary fluid union to the hydraulic characterization permeameter 56,(iii) observing the changes in suction and moisture content in thespecimen while fluid advances through the specimen, (iv) measure thefluid outflow rate to determine when steady-state flow conditions occur.This procedure may be repeated at different rotational velocities andfluid flow rates to define different hydraulic properties. The fluidretention curve may be determined from the hydraulic characterizationpermeameter 56 of the CPUS system by plotting the values of the averagesuction and average moisture content measured during the test. Thehydraulic conductivity function may be determined using the measuredgradient in suction with specimen height and the fluid flow rate.

The hydraulic characterization permeameter 56 of the CPUS system canalso be used for simpler tests, without instrumentation, to determinethe relationship between the suction and moisture content. In thissystem, an initially fluid-saturated specimen rests upon a supportingplate, and is spun in the centrifuge (not shown) at a constantrotational velocity. Flow of fluid occurs from the base of the specimenuntil the conditions within the specimen are in equilibrium with thepotential energy induced by the centrifuge (not shown). In fact, thepotential energy induced by the centrifuge (not shown) can be thought ofas an equivalent suction being imposed upon the specimen. After flowstops (i.e., equilibrium is reached), the specimen is weighed todetermine the amount of moisture that has flowed out of the specimen.This procedure may be repeated in several stages, each with an increasedcentrifuge rotational velocity. After the final testing stage, themoisture content of the specimen may be determined using an oven, andthe moisture content at each stage of the test may be back-calculated. Arelationship between suction and moisture content can be determined todefine the fluid retention curve.

Prototype Permeameter. FIG. 6 shows a cross sectional view of aprototype permeameter 70. Prototype is used to denote the scaledrelationship between a small-scale specimen in the centrifuge and alarge-scale earthen structure in the nature (e.g., dams, embankments,landfills, slopes, etc.). The prototype permeameter 70 is used tocharacterize the hydraulic properties of unsaturated soils as well as tomodel flow through unsaturated soil profiles with different depths. Theprototype permeameter 70 has the additional capability of measuring andinducing evaporation from the upper surface of the specimen to simulatenatural fluid flow processes. One embodiment of the prototypepermeameter 70 has a cylinder 58, which may be 12 inches tall with 6inches inside diameter and a 0.5 inch wall thickness. The inside heightwithin the prototype permeameter is 12 inches with a soil specimen (notshown) height of about 11 inches, allowing for about 1 inch at the topfor air space (not shown). However, the cylinder 58 may be between about0.5 and 24 inches tall with between about 4 to 8 inches inside diameterand between about 0.25 and 1 inch wall thickness. The cylinder may besteel with an acrylic window for visualization (not shown).

In operation, fluid connection 72 from an infusion pump (not shown)moves through the rotary fluid union and enters the prototypepermeameter 70. Centripetal force generated by the spinning centrifugeis used to accelerate fluid flow toward the distal portion 74 of theprototype permeameter 70. The prototype permeameter 70 has a fluidinflow distribution cap 34 to ensure even distribution of fluid over thesoil surface (not shown). The fluid inflow distribution cap 34 may havean o-ring seal (not shown) to the cylinder 58 to prevent fluid leakage.The cylinder 58 may have air ports (not shown) for air entry and airescape (e.g., two 0.25 inch NPT holes at a height of 11.5 inches fromthe base of the permeameter) to induce evaporation from the top surfaceof the soil sample (not shown). An outflow support disc 66 may be madefrom 0.5 inch steel or acrylic disc with honeycomb mesh of 1/32inchholes, which may also be sealed with an o-ring seal (not shown) to thecylinder 58 to prevent fluid leakage. However the outflow support disc66 may be between about 0.1 and 0.75 inches with a honeycomb mesh ofbetween 1/64 and 1 inch holes and constructed from metals, alloys,composites, polymers, plastics or similar materials and either coatedpartially, entirely or uncoated.

The prototype permeameter 70 has an external primary fluid outflowcollection reservoir(s) 76, with use of a fluid pressure transducer 68(PT) to measure the pressure in the fluid within the fluid outflowcollection reservoir(s) 76. A hole beneath the support disc (not shown)allows water to enter a primary outflow collection reservoir 76 withoutallowing fluid from flowing back into sample ((not shown) when acentrifuge (not shown) is at rest. A primary fluid outflow collectionreservoir 76 includes one or more ports 78 for the placement of a fluidpressure transducer (PT) 68 used to measure the volume of fluid outflow.The fluid outflow collection reservoir 76 is detachable for 1-gweighing. The primary outflow collection reservoir 76 may be connectedto a secondary expansion outflow collection reservoir (not shown). Oneor more secondary expansion outflow collection reservoir(s) (not shown)allows overflow from the primary outflow collection reservoir 76 forextended testing and may be located adjacent to the primary outflowcollection reservoir 76.

The prototype permeameter 70 includes a number of instrumentation holes(not shown). In one embodiment, e.g., a total of 18 holes (e.g., 0.5inch NPT) are placed along the cylinder 58. For example, the 18 holesmay include 3 circumferentially spaced arrays of 5 equally spacedvertical holes. In one example, arrays ports 80 include 3 arrays of 5ports (e.g., 2 inch spacing from the bottom of the permeameter) areused. The arrays ports 80 will be used for heat dissipation units 84,time domain reflectometry probes (not shown), and other instrumentation(e.g., tensiometers, temperature, etc.) (not shown). For example,typical TDR probe are 4.5 inches long, HDUs are 2.5 inches long, andtensiometers are 1 inch long, so the probes will be close to each other.Because of the close spacing, the vertical profiles may be placed at,e.g., 0 degrees, 90 degrees, and 180 degrees, with the TDR probe 82 inthe center and the HDU 84 and tensiometers 86 perpendicular as shown inFIG. 6B.

Additionally, the cylinder 90 may have a pinhole with a screw seal 88 isprovided to allow air escape (e.g., to prevent buildup of air pressureduring fluid flow into the outflow collection reservoir) and a vent hole88 located on the upper side of the collection reservoir to preventfluid leakage when centrifuge is at rest.

One or more fluid level holes may be placed at a height of 1 inch fromthe base, spaced 120 degrees circumferentially. The fluid level holesmay be used as an alternate boundary condition consisting of a fluidlevel maintained constant at the specimen base. A plug 78 in the bottomof the fluid outflow collection reservoir(s) 76 allows fluid toaccumulate in the specimen to the level of the fluid level holes. Fluidmay then spill over through the fluid level holes (not shown) into theoutflow collection cylinder (not shown).

One or more air flow holes 80 may also be included made for air flow,e.g., one for air inlet and the other for air outlet. The air flow hole92 may be located at a height of 11 inches above the top of the soillayer. The prototype permeameter 70 may also include a number ofmounting points (not shown) which allow the prototype permeameter 70 tobe mounted into the centrifuge (not shown). For sample visualization,one or more windows (e.g., acrylic) in upper channel of the drum may beincluded (not shown). To obtain images of the sample during flow, one ormore strobe lights (not shown) timed to the rotational velocity of thecentrifuge (not shown) may be positioned to visualize the samplein-flight. For example, a charge-coupled display (CCD) camera may beused for visualization.

A typical test in the prototype permeameter test may be conducted usinga procedure similar to that of the hydraulic characterizationpermeameter. The main differences would be the selection of a rotationalvelocity in the centrifuge (not shown) such that scaling relationshipscan be used to correlate the behavior of the specimen (model) to anequivalent earthen structure in the field prototype). Different from thehydraulic characterization permeameter 56, inflow may be stopped andevaporation may be induced by passing air through the air ports at thetop of the prototype permeameter 70. This will create an upward flow ofwater, which may be monitored using the heat dissipation units (notshown) and time domain reflectometry probes (not shown). Accordingly,infiltration and evaporation may be controlled to simulate weatherprocesses that may affect an earthen structure in the field.

FIGS. 7A-F show different permeameter configurations in a centrifuge 94.FIGS. 7A and 7B show top views of a prototype permeameter hanger 96 andof a characterization or shrink/swell permeameter environments 98 insidea centrifuge 94, respectively. FIGS. 7C and 7D show elevation views of aprototype permeameter hanger 96 and a characterization or shrink/swellpermeameter environments 98 inside a centrifuge 94, respectively. FIGS.7E and 7F show isometric views of a prototype permeameter 96 and ashrink/swell permeameter environments 98 inside a centrifuge 94,respectively.

The TDR cable tester and multiplexer (not shown) may be placed in thecenter of the centrifuge 94. A data acquisition system (not shown)within the centrifuge 94 is connected to the probes (not shown) and ordetection devices (not shown) placed along the permeameters to detectthe following variables: moisture content; suction; fluid inflow rate;fluid outflow rate (e.g., to verify steady-state fluid flow conditions);specimen weight (e.g., to measure evaporation); air temperature orrelative humidity; and/or specimen temperature. To measure thesevariables a number of instruments are used. For example, time domainreflectometry to measure moisture content (including a holding devicefor a cable tester and multiplexer); heat dissipation units to measure

suction (e.g., 4 for each permeameter); tensiometers to measure suction(e.g., 4 for each permeameter); thermocouple psychrometers to measuresuction (e.g., 4 for each permeameter); pressure transducer to measurefluid outflow rate measurement (e.g., 1 for each permeameter); anelectronic load cell or pressure transducer to measure measuringspecimen weight (e.g., 2 for each permeameter); a linearly variabledisplacement transformer to measure settlement measurements in theshrink/swell permeameter (e.g., 1 for each permeameter); and/orthermocouples to measure specimen and air temperatures (e.g., 3 for eachpermeameter). In this configuration, the data acquisition device uses atleast 32 channels and is capable of interacting with cable-testersoftware. A power supply in the centrifuge 94 is provided for alltransducers between 5 and 30 volts for operation, except for the TDRs(not shown). Although this embodiment uses 32 channels other embodimentsmay use different numbers of channels, e.g., 8, 16, 48 etc.

It will be understood that particular embodiments described herein areshown by way of illustration and not as limitations of the invention.The principal features of this invention can be employed in variousembodiments without departing from the scope of the invention. Thoseskilled in the art will recognize, or be able to ascertain using no morethan routine experimentation, numerous equivalents to the specificprocedures described herein. Such equivalents are considered to bewithin the scope of this invention and are covered by the claims.

All publications and patent applications mentioned in the specificationare indicative of the level of skill of those skilled in the art towhich this invention pertains. All publications and patent applicationsare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

All of the compositions and/or methods disclosed and claimed herein canbe made and executed without undue experimentation in light of thepresent disclosure. While the compositions and methods of this inventionhave been described in terms of preferred embodiments, it will beapparent to those of skill in the art that variations may be applied tothe compositions and/or methods and in the steps or in the sequence ofsteps of the method described herein without departing from the concept,spirit and scope of the invention. More specifically, it will beapparent that certain components which are both chemically andphysiologically related may be substituted for the components describedherein while the same or similar results would be achieved. All suchsimilar substitutes and modifications apparent to those skilled in theart are deemed to be within the spirit, scope and concept of theinvention as defined by the appended claims.

1-15. (canceled)
 16. A centrifuge permeameter comprising: a cylinderhaving at least one window for visual inspection positioned between ainflow end of the cylinder and a outflow end of the cylinder; a fluiddistribution cap disposed at the inflow end of the cylinder; a soilsample support cap disposed at the outflow end of the cylinder; aprimary fluid outflow collection reservoir disposed about the cylindercomprising one or more fluid pressure transducers to measure outflowvolume; and a pinhole to prevent build-up of air pressure in the primaryfluid outflow collection reservoir; wherein the permeameter is adaptedto operate within a centrifuge.
 17. The centrifuge permeameter of claim16, further comprising two or more ports disposed about the cylinder topermit contact between the two or more ports and the soil sample tomeasure a suction profile.
 18. The centrifuge permeameter of claim 16,further comprising one or more time domain reflectometry (TDR) probesgenerally perpendicular to, and at least partially within, the cylinderto measure the average moisture content in the soil sample.
 19. Thecentrifuge permeameter of claim 17, wherein the two or more ports areadapted to fit instrumentation comprising one or more time domainreflectometry (TDR) probe, one or more heat dissipation units (HDUs) andcombinations thereof.
 20. The centrifuge permeameter of claim 16,further comprises a secondary overflow fluid outflow collectionreservoir disposed within the chamber comprising: one or more fluidpressure transducers to measure outflow volume; and a pinhole to preventbuild-up of air pressure in the outflow reservoir.
 21. The centrifugepermeameter of claim 16, wherein the centrifuge permeameter furthercomprises an instrumentation module that continuously measures one ormore variables relevant to unsaturated fluid flow through soils whilethe centrifuge is in flight.
 22. The centrifuge permeameter of claim 21,wherein the instrumentation module nondestructively measures one or morevariables relevant to unsaturated fluid flow through soils while thecentrifuge is in flight.